A turbine shaft scale model heat engine fatigue test method

Abstract

The application discloses a turbine shaft scale-down piece hot machine fatigue experiment method, and belongs to the field of turbine shaft technology and material mechanical property testing. The application comprises a turbine shaft scale-down piece design method, a turbine shaft scale-down piece clamp design scheme method and a turbine shaft scale-down piece hot machine fatigue test system. The application uses an equal proportionally reduced simulation piece to equivalently perform stress state on a dangerous position of a turbine shaft structure, so as to characterize the fatigue performance of the turbine shaft, and can partially replace a component level examination test, shorten a structure design cycle and reduce component consumption. The application uses a design that the scale-down piece and the clamp loading axis are parallel but not collinear, so that the tensile-bending-torsional fatigue test is carried out on a tensile-torsional testing machine, the tensile and torsional loads of the testing machine are converted into tensile, bending and torsional loads, and the loads are applied to the scale-down piece. The application uses a bolt and a special-shaped end clamping mode to respectively transmit the tensile, bending and torsional loads, and the structure is simple and reliable.

Description

TECHNICAL FIELD

[0001] The present application relates to a turbine shaft scale model thermal mechanical fatigue test method, belonging to the field of aero-engine turbine shaft technology and material mechanical property testing, and is especially suitable for various turbine shaft scale models to carry out thermal mechanical fatigue tests under variable temperature conditions, including torsional load and in-phase proportional tension, bending load. BACKGROUND

[0002] Turbine shaft is one of the main parts of an aero-engine, which bears multiple loads such as tension, bending, torsion and high temperature during operation. Due to design and manufacturing reasons, combined with harsh working conditions, turbine shafts have early failure problems. Whether the turbine shaft can work normally under multiple loads directly determines whether the engine can serve normally, and finding out the safe service boundary of the turbine shaft is of great significance to national defense security.

[0003] Turbine shafts are expensive, and abandoning turbine shafts that have not reached their service life makes the daily use and maintenance cost of the engine extremely high. At the same time, turbine shafts bear multiple components such as turbine discs and turbine blades, and the replacement and detection procedures are complicated, which greatly affects the normal service of the aero-engine. If the safe service life boundary of the turbine shaft can be found out, the overhaul interval of the engine can be extended, and the replacement amount of the turbine shaft can be reduced, which has great economic and security value.

[0004] The aero-engine turbine shaft is large in size and runs through the engine compressor-combustor-turbine structure. The temperature load and stress state of each part differ greatly and change complexly with the flight state. If a structural part is directly used for testing, it is difficult to apply the load, and it is difficult to obtain ideal results. At the same time, the cost of complete structural parts is high, and it is difficult to obtain.

[0005] Hunan University's Fan Cahe, Chen Zhenhua, and others used a 1:5 hollow shaft scale model in their paper "Preparation Process, Mechanism and Performance Research of Aluminum Alloy Hollow Shaft for High-speed Locomotive" to study the microstructure and mechanical property evolution law of the scale model under different process conditions, and confirmed the feasibility of using scale models for mechanical property testing. However, due to the limitations of the loading conditions, only room temperature tensile properties, rotating bending fatigue and static strength tests of the hollow shaft scale model were carried out. Limited by the integrated loading conditions, the synchronous composite loading fatigue test of tension, bending and torsion could not be carried out.

[0006] Therefore, it is feasible and necessary to invent a thermal mechanical fatigue test method for a scale model of an aero-engine turbine shaft containing synchronous composite loading of tension, bending and torsion. SUMMARY

[0007] The application aims to provide a turbine shaft scale model thermal fatigue test method, which uses a scale model to examine the mechanical properties of an aero-engine turbine shaft under synchronous combined loading of tension, bending and torsion, and is used for fatigue performance evaluation of aero-engine turbine shafts and is also applicable to other shaft parts under tensile, bending and torsional load.

[0008] The application is achieved by the following technical scheme.

[0009] The application further provides a turbine shaft scale model design method, which specifically comprises the following steps:

[0010] a) geometrically modeling and meshing the turbine shaft to be examined, taking the load borne by the turbine shaft during service as a boundary condition and applying corresponding constraints, and then calculating the service stress field, temperature field and strain field of the turbine shaft;

[0011] b) determining the dangerous position of the turbine shaft to be examined according to the actual service failure position and the stress field, temperature field and strain field obtained in step a), and cutting off a 20cm-long part of the turbine shaft before and after the dangerous position as a dangerous section;

[0012] c) proportionally reducing the geometric model of the dangerous section determined in step b), and determining the reduction ratio in combination with an induction heating coil and scale model processing conditions;

[0013] d) increasing a transition fillet and a special-shaped end at both ends of the proportionally reduced turbine shaft dangerous section through a geometric optimization method, and machining a through hole on the special-shaped end, wherein the special-shaped end is in the form of a cross-shaped star with a fillet, is used for clamping with a clamp to transmit a torsional load, and the longer the circumference, the more stable the torsional load, and the circumference formula is:

[0014]

[0015] wherein La is the circumference of the special-shaped end, r1 is the outer diameter of the transition fillet on the scale model shaft, r2 is the radius of the fillet of the special-shaped end, and l1 is the center distance between r1 and r2;

[0016] The application further provides a turbine shaft scale model clamp design scheme, which specifically comprises the following steps:

[0017] a) designing a rod-shaped clamping end with a corresponding size according to the model of a material tension-torsion testing machine, and designing a disc coaxial with the clamping end and having a radius greater than the maximum width of the special-shaped end according to the size of the special-shaped end of the turbine shaft scale model;

[0018] b) obtaining the service load of the turbine shaft, taking L(m) = bending moment M(Nm) / axial tension F(N), and L is the center distance between the shaft line of the clamp rod end and the shaft line of the turbine shaft scale model, so that a bending moment of M is generated on the scale model while the tension F is applied;

[0019] c) machining a special-shaped groove and a through hole corresponding to the shape and size of the special-shaped end on the disc for fixing the turbine shaft scale model, the center of the special-shaped groove is at a distance L from the center of the disc, and special-shaped grooves with different center distances are machined in other directions of the disc to realize loading of different bending moments and fully utilize the value of the clamp;

[0020] Further, the present application provides a turbine shaft scale model thermal mechanical fatigue test system comprising a material tensile-torsion testing machine, a clamp, a load control system and a temperature control system.

[0021] The material tensile-torsion testing machine can apply axial tensile load and torsional load around the shaft; the load control system comprises a load control server, a load sensor and a displacement sensor; the temperature control system comprises a high-pressure gas source, a cold gas nozzle, an induction heating coil, a thermocouple and a temperature control box. The turbine shaft scale model is installed on the clamp, the clamp is clamped on the material tensile-torsion testing machine, and the load, displacement deformation and temperature of the turbine shaft scale model are collected through the load sensor, the displacement sensor and the thermocouple and fed back to the load control server and the temperature control box. The material tensile-torsion testing machine, the load sensor, the displacement sensor and the load control server are connected, the induction heating coil is sleeved around the turbine shaft scale model, and the induction heating coil, the thermocouple, the high-pressure gas source and the cold gas nozzle are connected with the temperature control box.

[0022] Preferably, the clamp comprises two clamping units, each clamping unit comprising a main chuck, a bolt and a nut, the surface of one end of the main chuck being provided with a special-shaped groove type sample mounting area matching the shape of the end of the turbine shaft scale model, the other end being a round bar, the end face of the sample mounting area being provided with four through holes corresponding to the through hole positions on the turbine shaft scale model, the bolt being passed through the through hole to the upper surface of the main chuck and being fastened with the nut to complete the connection of the turbine shaft scale model and the main clamp, and the end of the round bar being used for connecting with the material tensile-torsion testing machine, the turbine shaft scale model being fixed by the two clamping units in opposite directions when in use, the axis of the end of the round bar being parallel to but not collinear with the axis of the scale model to generate a bending load and achieve the effect of loading tensile, bending and torsional load on the material tensile-torsion testing machine.

[0023] The load sensor and the displacement sensor are installed on the cross beam of the material tensile-torsion testing machine, the cold gas nozzle and the induction heating coil are fixed on the temperature control platform, and the thermocouple is installed on the turbine shaft scale model.

[0024] The present application also provides a method for carrying out turbine shaft scale model thermal mechanical fatigue test by using the above system, comprising the following steps:

[0025] 1) According to the design scheme of the scale model, a test piece is cut from a homogeneous raw material or blank with the same chemical composition and heat treatment process as the turbine shaft, and a high-precision numerical control lathe or other equipment is used to process the test piece into a turbine shaft scale model with special-shaped connecting ends and transition fillets at both ends;

[0026] 2) According to the jig design scheme, the jig is processed from the high-temperature alloy blank, bolts and nuts are obtained, and the jig with a special-shaped groove is obtained;

[0027] 3) The scaled-down part processed in step 1) is sleeved into the induction heating coil and then installed into the jig processed in step 2), the jig round bar end is clamped at the chuck of the material tension-torsion testing machine, the test position of the scaled-down part is ensured in the middle of the induction heating coil, and the clamping of the turbine shaft scaled-down part is completed;

[0028] 4) The thermocouple is fixed at the test position of the turbine shaft scaled-down part, the cold gas nozzle is adjusted to be aligned with the test position of the scaled-down part, and the load sensor and the displacement sensor equipped in the testing machine are checked;

[0029] 5) The temperature load spectrum is input through the temperature control box, the heating temperature range is 25-1300 DEG C, the load control server and the material tension-torsion testing machine are started, the load control server executes the pre-set loading waveform on the material tension-torsion testing machine, the load sensor and the displacement sensor collect the load and strain data of the turbine shaft scaled-down part, and the data is transmitted to the load control server, and the testing is completed after the turbine shaft scaled-down part is broken;

[0030] 6) The temperature control box is turned off, the turbine shaft scaled-down part is taken down after the temperature is reduced to room temperature, and the load, deformation and life data of the turbine shaft scaled-down part in the load control server are saved.

[0031] Advantageous effects:

[0032] 1. The turbine shaft scaled-down part of the present application can ensure the equivalence of the stress state of the scaled-down part and the test position of the turbine shaft, simplify the structure, reduce the difficulty of load loading, and improve the test precision compared with using the whole structure of the turbine shaft for testing;

[0033] 2. The present application designs a test tool that is parallel to the load loading shaft but not collinear, realizes the loading of tensile, bending and torsional load on the material tension-torsion testing machine, and can be used for carrying out tensile-bending-torsional fatigue test under room temperature, high temperature and variable temperature conditions, and reduces the test threshold;

[0034] 3. The special jig for the turbine shaft scaled-down part of the present application realizes the transmission of tensile and bending load through bolt fixation, realizes the transmission of torsional load through a special-shaped end structure, avoids using a complex structure, is simple and reliable, and integrates special-shaped grooves with different center distances L on one set of jig to meet the loading demand of different bending moment / tension ratios, and reduces the test cost. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The jig design process of the present application;

[0036] Figure 2 This is a schematic diagram of the thermal fatigue testing system for the turbine shaft scaling component of the present invention;

[0037] Figure 3 For a certain type of aircraft engine turbine shaft;

[0038] Figure 4 A three-dimensional drawing of the turbine shaft reduction component designed for this invention;

[0039] Figure 5 A 3D view of the main chuck of the fixture designed for this invention;

[0040] Figure 6 A 3D schematic diagram of a special tooling fixture for turbine shaft scaling components;

[0041] Figure 7 Load spectrum for tensile, bending and torsional fatigue tests of a scaled-down turbine shaft component of a certain type of aero-engine;

[0042] Figure 8 This is a stress distribution cloud diagram of the turbine shaft scaling component of the present invention under test load;

[0043] Figure 9 This is a comparison curve of the stress normalization between the test position of the turbine shaft reduction component of the present invention and the original structure.

[0044] Among them, 1—material tension and torsion testing machine, 2—clamping unit, 3—induction heating coil, 4—temperature control box, 5—high pressure air source, 6—load sensor, 7—displacement sensor, 8—contact thermocouple, 9—turbine shaft scaled-down part, 10—high pressure cold air nozzle, 11—load control server, 901—scaled-down part irregular end, 902—scaled-down part test position, 903—scaled-down part transition fillet, 904—scaled-down part bolt hole, 201—scaled-down part fixture, 202—bolt and nut, 2011—fixture clamping end, 2012—irregular groove 1, 2013—irregular groove 2, 2014—irregular groove 3. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0046] This invention provides a method for thermodynamic fatigue testing of scaled-down turbine shaft components. The specific implementation of this invention is described below using a turbine shaft from a certain type of aero-engine as an example:

[0047] refer to Figure 1 The experimental method and procedure described in the text first take a certain type of aero-engine turbine shaft as an example to analyze its geometric characteristics, such as... Figure 3As shown, the turbine shaft length is 1590 mm, the large end port diameter is 159.80 mm, and the small end port diameter is 124 mm. The inner hole is composed of two sections with a diameter of 85 mm and a hole depth of 1290 mm, and a diameter of 66 mm and a hole depth of 300 mm. There are 6 φ12 circumferential holes, bosses between unequal diameter shaft sections, and wheel discs distributed on the shaft. According to the finite element simulation results and the actual service damage position, the circumferential hole (circled) is selected as the evaluation position, and the stress is 769 MPa.

[0048] The turbine shaft evaluation position diameter is 124 mm, the induction heating coil 3 in the thermal machine fatigue test system is 50 mm long, and can accommodate a component with a diameter of 70 mm. Therefore, the scale of the turbine shaft: scale of the scale piece is determined to be 4:1.

[0049] The profiled end 901 of the turbine shaft scale piece 9 is designed, and the circumference formula is:

[0050]

[0051] In the formula, La is the circumference of the profiled end 901, r1 is the outer diameter of the transition fillet 903 on the shaft of the scale piece 9, r2 is the fillet radius of the profiled end 901, and l1 is the distance between the centers of r1 and r2;

[0052] The partial derivative of the profiled end 901 circumference La with respect to l1 is obtained as

[0053]

[0054] Since l1>r1>r2 in this example, dLa / dl1 is always greater than 0, that is, the circumference of the profiled end 901 monotonically increases with l1.

[0055] The partial derivative of the profiled end 901 circumference La with respect to r1 is obtained as

[0056]

[0057] Since l1>r1>r2 in this example, dLa / dr1 is always less than 0, that is, the circumference of the profiled end 901 monotonically decreases with r1.

[0058] The partial derivative of the profiled end 901 circumference La with respect to r2 is obtained as

[0059]

[0060] Since l1>r1>r2 in this example, dLa / dr2 is always greater than 0, that is, the circumference of the profiled end 901 monotonically increases with r2.

[0061] The special-shaped end fillet with a radius of r2 is not contained by the transition fillet 903 on the shaft of the reduced section part with a radius of r1, and 20<=r1<=l1 needs to be met, and is further limited by the size of the coil and the reduced section part, 20<=l1<=36 and r2<=36-l1. Three maximum points are obtained by calculating the zero points of the partial derivative formula of the circumference La of the special-shaped end 901, the maximum circumference corresponding to r1r2l1 is selected by comparing the three maximum points, and the special-shaped end size is obtained after the integer is taken: r1=20, r2=6, and l1=30. That is, the radius of the transition fillet 903 is 4.5 mm, the outer diameter of the shaft fillet of the reduced section part is 40 mm, the radius of the special-shaped end fillet is 6 mm, the center distance is 30 mm, the thickness of the special-shaped end is 10 mm, and the reduced section part is designed. At this time, the outer circumference La of the reduced section part is 430.91 mm, the side area is 4309 mm 2 , and the equivalent pressure is 73.64 Mpa when the torque is transmitted, which is beneficial to realize stable loading of the torque.

[0062] As shown in Figure 4 , the turbine shaft reduced section part 9 is designed to be 60 mm long, the examination section has an outer diameter of 31 mm and an inner diameter of 16.5 mm, the examination circumferential hole 902 has a diameter of 3 mm, and the six holes are distributed along the circumference and located in the middle of the reduced section part. The four bolt holes 904 are distributed on the circumference with a radius of 26 mm.

[0063] The loads to which the turbine shaft is subjected during service are obtained, respectively: torque T=33000 Nm, axial force F=150 kN, and bending moment M=60000 Nm. The center distance L between the special-shaped groove 2014 on the clamp 201 and the center of the loading shaft is M / L=40 mm, and the special-shaped grooves 2012 and 2013 with L of 48 mm and 52 mm are processed for different bending moment load tests. The design of the turbine shaft reduced section part special clamp 201 is shown in Figure 5 .

[0064] The turbine shaft reduced section part thermal-mechanical fatigue test system provided by the application is used to carry out fatigue tests on the turbine shaft reduced section part under the action of thermal-mechanical loads:

[0065] Firstly, referring to Figure 2 , Figure 4 , Figure 5 , Figure 6 , the turbine shaft reduced section part 9 is sleeved into the induction heating coil 3, the special-shaped end 901 of the turbine shaft reduced section part 9 is installed in the special-shaped groove 2014 of the main clamp 201 of the lower clamping unit 2 according to the structure shown in Figure 6 , and the bolt and nut 202 are screwed into the through hole 904 and tightened, so as to ensure that the turbine shaft reduced section part 9 is stably connected with the clamping unit 2. The upper end of the turbine shaft reduced section part 9 is installed on the upper clamping unit 2 by using the same scheme, and after the installation is completed, the clamping end 2011 of the main clamp 201 is clamped on the clamp of the material tension-torsion testing machine 1, and the clamping of the turbine shaft reduced section part 9 is completed.

[0066] Second step, the contact thermocouple 8 is fixed on the turbine shaft scale 9 test site circumferential hole 902 with asbestos wire, used to detect the turbine shaft scale 9 temperature and feedback to the temperature control box 4. Adjust the position of the high pressure cold gas nozzle 10, and align it with the turbine shaft scale 9 test site 902.

[0067] Third step, open the high pressure gas source 5, start the material tension-torsion testing machine 1, load control server 11 and temperature control box 4. The temperature control box 4 controls the induction heating coil 3 and the high pressure cold gas nozzle 10 to execute the pre-set temperature load loading program, and the load control server 11 controls the material tension-torsion testing machine 1 to execute the pre-set tension-torsion load loading program. The load spectrum is shown in Figure 7 , the load level is 1 / 4 of the original structure. The high-precision load sensor 6 and displacement sensor 7 are used to collect the load and displacement data of the turbine shaft scale 9, and transmit them to the load control server 11, until the turbine shaft scale 9 breaks, which is considered as the end of the tension-bending-torsion fatigue test.

[0068] Fourth step, after the test is completed, the temperature control box 4 is turned off, and the turbine shaft scale 9 is removed after the temperature drops to room temperature. The collected load, displacement and test piece life data are saved, and the load control server 11 is turned off.

[0069] Figure 8 In order to use the finite element method to analyze the stress of the turbine shaft scale 9 of the present application, the unit is MPa, it can be found that the maximum stress appears at the test site circumferential hole 902, which is consistent with the actual stress state of the turbine shaft.

[0070] The stress distribution normalization results of the scale and the original structure of the turbine shaft with hole depth are as follows Figure 9 , the fitting degree is good, especially the starting round corner position where the angular crack is easy to grow, which well simulates and approximates the load characteristics of the original structure. The scale design scheme is feasible, the fatigue life dispersion is small after the test, and the fatigue test result is reliable.

[0071] The above specific description further describes the purpose, technical scheme and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the invention and does not limit the protection scope of the invention. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the invention shall be included in the protection scope of the invention.

Claims

1. A method for thermodynamic fatigue testing of a turbine shaft scaling component, characterized in that: Includes the following steps: Step 1: Determine the turbine shaft reduction ratio component with a rounded corner cross-shaped irregular end structure; a) Perform geometric modeling and meshing of the turbine shaft under test, use the loads on the turbine shaft during service as boundary conditions, and apply corresponding constraints; then, calculate the stress field, temperature field, and strain field of the turbine shaft during service. b) Based on the actual service failure location and the stress field, temperature field and strain field obtained in step a, determine the critical location of the turbine shaft to be tested; cut off a section of the turbine shaft 20cm before and after the critical location as the critical section; c) The geometric model of the dangerous section determined in step b is scaled down proportionally. The scaling down ratio is determined in combination with the induction heating coil and the processing conditions of the scaled-down part. d) Using geometric optimization methods, irregular ends and transition fillets are added to both ends of the proportionally scaled-down critical section of the turbine shaft, and multiple through holes are machined on the irregular ends. The irregular ends are in the form of a cross-shaped star with rounded corners, used for clamping with fixtures to transfer torsional loads. The longer the perimeter of the cross-shaped star, the more stable the application of torsional loads. The formula for its perimeter is: In the formula, La is the circumference of the irregular end, r1 is the outer diameter of the fillet on the shaft of the scaled part, r2 is the radius of the fillet at the irregular end, and l1 is the distance between the centers of r1 and r2. Step 2: Tooling and Fixture Design a) Design a rod-shaped clamping end of the corresponding size according to the model of the material tension and torsion testing machine chuck. Refer to the size of the irregular end of the turbine shaft scaled part, design a disc and make it coaxial with the clamping end, with a radius greater than the maximum width of the irregular end. b) Obtain the service load of the turbine shaft, take L(m) = bending moment M(Nm) / axial tension F(N), where L is the center distance between the axis of the end of the clamping round bar and the axis of the turbine shaft scaled part. Thus, while applying tension F, a bending moment of magnitude M is generated on the scaled part. c) Machining irregular grooves and through holes on the disk that correspond to the shape and size of the irregular end for fixing the turbine shaft reduction component. The distance between the center of the irregular groove and the center of the disk is L. At the same time, machining irregular grooves with different center distances in other directions of the disk to achieve different bending moment loading and make full use of the value of the fixture. Step 3: Using the fixture from Step 2, hold the scaled-down part from Step 1 and conduct a thermomechanical fatigue test. a) After the scaled-down part from step one is inserted into the induction heating coil, it is installed into the fixture from step two. The round bar end of the fixture is installed into the chuck of the material tensile and torsion testing machine and clamped to ensure that the test position of the scaled-down part is in the middle of the induction heating coil, thus completing the clamping of the turbine shaft scaled-down part. b) Fix the thermocouple to the test position of the turbine shaft scaled-down component, adjust the cold air nozzle to align with the test position of the scaled-down component, and check the load sensor and displacement sensor equipped on the testing machine. c) Input the temperature load spectrum through the temperature control box. The heating temperature range is 25℃~1300℃. Start the load control server and material tension and torsion testing machine to start the test until the turbine shaft reduction ratio component breaks.

2. An apparatus for implementing the method as described in claim 1, characterized in that: include: The system includes a material tensile and torsion testing machine, a fixture, an induction heating coil, a temperature control box, a high-pressure gas source, a load sensor, a displacement sensor, a contact thermocouple, a turbine shaft scaled-down component, a high-pressure cold air nozzle, and a load control server. The turbine shaft scaled-down component is mounted on the fixture, which is clamped onto the material tensile and torsion testing machine. The load sensor, displacement sensor, and contact thermocouple collect data on the load, displacement deformation, and temperature of the turbine shaft scaled-down component and feed this data back to the load control server and the temperature control box. The material tensile and torsion testing machine, load sensor, and displacement sensor are connected to the load control server. The induction heating coil is fitted around the turbine shaft scaled-down component. The high-pressure cold air nozzle is aligned with the test position of the scaled-down component. The induction heating coil, contact thermocouple, high-pressure gas source, and high-pressure cold air nozzle are all connected to the temperature control box.

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